Roll-up door assembly, and blow molded panel therefor

ABSTRACT

A roll-up door has a plurality of panels and a plurality of roller assemblies mounted to ends of the panels for mounting the panels in channels. At least some of the panels are formed of blow-molded thermoplastic material and have a relatively flat outside face and an inside face including open channels that extend longitudinally and transversely on the panel. A reinforced panel of thermoplastic material is made by blow molding a panel with a thermoplastic material to form a relatively flat outside face and a ribbed inside face, and with elongated channels along upper and lower portions thereof. The panel may be trimmed while it is still warm to open the channels at one end. While the panel is still warm, reinforcing members may be inserted into the elongated channels. The panels may be cooled to shrink the channels onto the reinforcing members.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/422,647, filed Apr. 13, 2009, now U.S. Pat. No. 8,448,689, issued May28, 2013, which claims the benefit of U.S. provisional application Ser.No. 61/044,711, filed Apr. 14, 2008, which is incorporated herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to roll-up door assemblies. In one of its aspects,the invention relates to blow molded panels for use in roll-up doors. Inanother of its aspects, the invention relates to molded plastic panelsthat simulate wood panels and are interchangeable with wood panels inroll-up doors. In still another of its aspects, the invention relates toa roll-up door assembly formed of blow molded plastic panels. In anotherof its aspects, the invention relates to a method of making a blowmolded panel for use in a roll-up door assembly.

2. Description of the Related Art

Trailers for use with semi-tractors and trucks, which can be constructedseparately from the semi-tractor or truck and attached thereto orconstructed integrally with the semi-tractor or truck, have long usedroll-up doors at an inside opening of the trailer to control access toan interior of the trailer. Roll-up doors are often preferred oververtically-hinged, outwardly-swinging doors because the roll-up doorsoperate within the physical space already occupied by the trailer and donot require space beyond the trailer. The roll-up door is moveablebetween an opened position and a closed position while being maintainedentirely within the interior of the trailer, whereas the swinging doorsrequire room along the sides of the trailer to swing from a closedposition to an opened position. If the trailers are to be parkedside-by-side, the swinging doors must be opened prior to parking thetrailer, or the trailers must be parked far enough apart to permit thedoors to swing from the closed position to the opened position, both ofwhich are an inconvenience to the operator.

Roll-up doors typically comprise multiple panels, stacked edgewise oneatop the other. The adjacent edges are connected together with hinges toform the entire door so that the panels can pivot with respect to eachother. The hinges are normally located on or near the adjacentlongitudinal edges of the panels. There are generally two main types ofhinged structures that can be categorized by the direction in which thepanels must be assembled relative to the longitudinal axis of thepanels. One hinge structure requires that the panels be slid laterally(in the same direction as the longitudinal axis) to hingedlycouple/uncouple the panels. Another structure requires that the panelsbe moved to transversely or perpendicular to the longitudinal edge tohingedly couple/uncouple the panels.

Each panel usually includes a roller assembly near each of the oppositelatitudinal edges. Each roller assembly comprises an axle that rotatablysupports a roller or wheel. The axle is mounted to the panel directlyor, alternatively, through a hinge positioned adjacent or near thelatitudinal edge. The roller is received within a track mounted withinthe interior of the trailer near the inside opening. As the door israised from the closed position to the opened position, the rollerstravel along the track to move the panels from a vertical positionclosing the inside opening of the trailer through a 90° curved sectionto a horizontal position overlying the interior of the trailer andexposing the inside opening of the trailer. The panels rotate relativeto each other as needed about their respective hinges. The panels areconstrained in their movement by the receipt of the rollers within thetrack. Thus, the maximum angle of rotation between any two panels can becontrolled by the arc of the track.

Roll-up doors have several known problems or disadvantages. Many roll-updoors have panels that are made entirely of solid material, such aswood. The resulting door is exceptionally heavy and requirescounter-balancing springs to lift and close the door. Thecounter-balancing springs reduce the usable volume of the trailer, whichis highly undesirable given the great value placed upon usable volumefor a trailer. In addition, the panels as well as the counterbalancingspring add to the trailer undesirable weight which adversely affectsfuel efficiency and thus profits.

Attempts to address this problem have focused on using lighter weightmaterials, especially extruded plastics. The resulting extruded panelsare relative light in weight, but they often require special or complexhinge systems and special structural stiffening to accommodate themounting of the roll-up door hardware such as handles and latchassemblies.

Many roll-up doors are often time-consuming to repair. When a roll-updoor is damaged, usually the repair is accomplished by merely replacingone of the multiple panels. Unfortunately, some plastic roll-up doorshave a panel and hinge configuration that requires the removal ofmultiple or all of the panels to replace the damaged panel. Panels thathave hinges that require the lateral sliding of the panels for assemblyfurther exacerbate the replacement of a single panel in that all of thepanels preceding the damaged panel must be removed from the tracksbefore the damaged panel can be laterally slid and uncoupled from theadjacent panels. However, current wood panel doors do not require acomplete disassembly of all panels and can usually be repaired byremoving the damaged panel and replacing it with a new wood panel butnot with a plastic panel.

U.S. Pat. No. 3,980,123 to Vago discloses using blow molded panelsections formed of polyethylene in garage doors and the like. The panelsare mounted in a rigid framework that include horizontal rail supportsspanning the length of the door and connected to vertical stile supportswhich span the height of the door. The horizontal rails protect the topand bottom sides of the panels and the vertical stile supports arehinged together to form the door. The hinges on the sides of the doorinclude rollers movably mountable in tracks of an aluminum door frame.The panels include indentations on an inside wall for strengtheningpurposes. Dead air spaces are formed as cavities during blow-moldingthrough the shaping of an outside wall with respect to the inside wall.

U.S. Pat. No. 6,826,887 to Skov discloses a blow-molded panel for use ina variety of applications, namely in forming storage units. The panelincludes lateral slots for enhancing the structural integrity of thepanel. The panel also includes a plurality of transverse ribs extendingthrough the lateral slots for additional strengthening.

U.S. Pat. No. 4,762,379 to Beam et al. discloses blow-molding a panelcomprising a plurality of depressions in a rear wall that extend to afront wall and that are fused thereto for structural rigidity. The panelis formed by blow molding in a mold cavity formed by the engagement of afirst mold plate and a second mold plate. Multiple projections on thesecond mold plate are used to form the depressions during the moldingprocess. Due to the restriction of the mold cavity by the projections, aplurality of blow needles project through the second mold plate suchthat air can be blown into each section created by the projections.

U.S. Pat. No. 7,210,277 to Steed discloses blow molding panels for usein a partition system for outdoor structures such as fences and sheds.The panels include edges with steel reinforcements. The partitions alsohave patterns on both sides formed by rows and columns of depressionsthat extend towards or engage an opposing surface. The patterns on bothsides of the partitions include one or more depressions and thedepressions are generally aligned so that a depression on one side of apanel is aligned with a depression on the other side of the panel. Inaddition, the patterns on the panels include grooves, and thedepressions are formed at the intersection of the grooves. Thedepressions are integrally formed in the panels are said to beconfigured to increase the strength of the panels. Because thedepressions are formed on both sides of the panel, the opposing sides ofthe panel may have generally the same pattern.

United States Patent Application Publication No. 2007/0209295 to Moweret al. discloses a shed comprising blow-molded panel walls. The wallscan include reinforcements to provide greater strength, rigidity, impactresistance, resilience and/or ability to prevent deformation. In orderto reinforce the panels, the reinforcements can have differentcapabilities or characteristics than the panels, such as differentstrength, resilience, compression and/or tension capabilities that thepanels, and the reinforcements may be arranged or configured to maximizethe strengths or characteristics of the thereof.

U.S. Pat. No. 6,955,206 to Mullet et al. discloses a sectional doorcomprising a plurality of panels formed by extrusion. The door cancontain reinforcing members in form of tubes, which can be inserted intothe panels after the panels are extruded and extended across the entirewidth of the panels. In addition, the tubes are exposed at both ends andform journals for axles of wheels. U.S. Pat. No. 6,672,362 is in thesame family as '206 to Mullet et al. and discloses a similar panelconstruction.

SUMMARY OF THE INVENTION

According to the invention, a roll-up door assembly comprises aplurality of panels joined together at the edges thereof with hinges.The roll-up door further comprises roller assemblies mounted to ends ofthe panels for mounting the panels in channels for movement between anupper position and a lower position. At least some of the panels areformed of blow-molded thermoplastic material wherein the panels have arelatively flat outside face and an inside face, which is characterizedby ribs that extend longitudinally and transversely on the panel.

The horizontal ribs can be formed by open, longitudinally extendingchannels that extend toward the outside wall and at least some of thelongitudinally-extending channels are fused to the outside wall of thepanels. The vertical ribs can intersect the horizontal ribs and theopen, longitudinally extending channels.

The hinges can be mounted to the thermoplastic blow-molded panels withfasteners that penetrate the thermoplastic blow-molded panels.

In one embodiment, the panels can have elongated hollow channels thatextend along the at least one of the upper and lower portions of thepanel and reinforcing members of a material stiffer than thethermoplastic material are retained in the elongated hollow channels. Inone embodiment, the fasteners penetrate the elongated channels. Inaddition, the fasteners can be rivets.

In a preferred embodiment, the reinforcing members can be frictionallyretained in the elongated channels by press fit into the elongatedhollow channels. In another embodiment, the reinforcing members can befrictionally retained in the elongated channels by shrink fitting theelongated hollow channels onto the reinforcing members.

Preferably, the elongated hollow channels can be formed along both theupper and lower portions of the panel, and both of the elongated hollowchannels can have reinforcing members therein.

In another embodiment, the reinforcing members can be formed of arelatively stiff metal or of a relatively rigid plastic material.

Typically, at least some of the hinges can be positioned at the sidewalls of the panels and these hinges can have sockets and the rollerassemblies mounted in the sockets.

Further according to the invention, a panel for use in a roll-up doorassembly comprising a plurality of panels directly joined together attop and bottom portions thereof with hinges and roller assembliesmounted to the panels for mounting the panels in channels for movementbetween an upper position and a lower position, can be formed ofthermoplastic material that is blow-molded into a hollow form that has arelatively flat outside wall and an inside wall. The inside wall can becharacterized by longitudinal ribs formed by open, longitudinallyextending channels that extend toward the outside wall and at least someof the longitudinally-extending channels are fused to the outside wallof the panels. Further, the panel can include elongated hollow channelsthat extend along the top and bottom portions of the panel, andreinforcing members of a material stiffer than the thermoplasticmaterial frictionally retained in the elongated hollow channels.

In one embodiment, the inside wall is further characterized by verticalribs that intersect the horizontal ribs and the open, longitudinallyextending channels.

In addition, the elongated hollow channels are shrunk fit onto thereinforcing members to frictionally retain the reinforcing members inthe hollow channels.

The reinforcing members can be press fit into the elongated hollowchannels to frictionally retain the reinforcing members in the hollowchannels.

In addition, the reinforcing members can be formed of a relatively stiffmetal or a rigid plastic.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an inside perspective view of a trailer incorporating aroll-up door according to the invention, with the roll-up doorcomprising multiple, hingedly-coupled panels moveably mounted within atrack.

FIG. 2 is a perspective view of the inside of a roll-up door assemblyillustrated in FIG. 1.

FIG. 3 is an enlarged view of the circled portion of FIG. 2 identifiedas III and showing an outer hinge receiving a roller assembly.

FIG. 3A is a partial cross-sectional view through lines 3A-3A of FIG. 3.

FIG. 4 is a perspective view of a panel that is used in the roll-up doorassembly illustrated in FIGS. 1 and 2.

FIG. 5 is a sectional view of the panel of FIG. 3 taken along line 4-4of FIG. 3.

FIG. 6 is a schematic diagram of a method of making a roll up door panelaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a conventional trailer 100 for attachment to orincorporation in a semi-tractor or truck incorporates a roll-up door 44according to the invention. The trailer 100 is of a well-known designand comprises opposing sidewalls 114, 116 connected at respective upperends by a top wall 118 and at respective lower ends by a bottom wall120. The top wall 118, bottom wall 120, and sidewalls 114, 116collectively define an inside opening 122 that is bounded by aperipheral frame 124. The roll-up door 44 is mounted to the trailer 100such that the roll-up door 44 closes the inside opening 122 when theroll-up door is in a lowered or closed position as illustrated inFIG. 1. A latch and handle assembly 126 is provided for locking theroll-up door 44 in the closed position.

Referring now to FIGS. 2-4, a plurality of panels 10 can be assembledtogether to form the roll-up door 44. Each of the panels 10 comprises aninside wall 12, an outside wall 14, two end walls 16, a top wall 18, anda bottom wall 19. The inside walls 12 of the panels 10 can constitute aninside wall of the door 44. The panels 10 are interconnected at theirtop walls 18 and bottom walls 19 by conventional inner hinges 56 andouter hinges 50 such that the panels 10 can move at an angle to oneanother to effect the rolling up of the door 44. Inner hinges 56 andouter hinges 50 are attached to the panels 10 by inner rivets 58 andouter rivets 52, respectively. The inner rivets 58 and the outer rivets52 extend through the inside wall 12 of the panel 10 at upper portions46 and lower portions 48 of adjacent panels. See FIG. 3A.

As shown in detail in FIG. 3, two conventional roller assemblies 36 aremounted to opposite sides of each of the panels 10 through the outerhinges 50. The outer hinges 50 each comprise a hinge body 53substantially similar to a conventional hinge body. The outer hinges 50further comprise a cap plate 54 adapted for connection to the hinge body53 via bolts 55. The cap plate 54 has a socket that receives an axle ofthe roller assembly 36 to mount the roller assembly to the outer hinge50. Once mounted to the door 44, rollers of the roller assemblies 36 canbe positioned within channels formed by tracks (not shown) framing theopening 122 on opposite sides thereof such that the door 44 can berolled up and down between the closed position illustrated in FIG. 1 andan upper or open position (not shown) when the door 44 is substantiallyhorizontal overlying the interior of the trailer 100.

The door 44 further includes a bracket 60 of the latch and handleassembly 126 attached to the lowermost panel 10 of the door 44 at thebottom wall 19 thereof by any suitable means, such as bracket rivets 61(FIG. 2) that extend through the inside wall 12 and outside wall 14. Thebracket 60 and bracket rivets 61 attach the latch and handle assembly126 to the door 44 to facilitate movement of the door 44 between theclosed position and open position when a user applies an upward ordownward force to the latch and handle assembly 126. Liners 62 can alsobe attached to the top wall 18 and bottom wall 19 of the uppermost andlowermost panels 10, respectively, of the door 44 to produce a moreairtight enclosure. The liners 62 can be sized to extend between thelongitudinal edges of the inside wall 12 and outside wall 14 to entirelycover the top wall 18 of the uppermost panel 10 and the bottom wall 19of the lowermost panel 10. It is also possible to interconnect panels 10with other types of panels to form the door. Conventional wood panelscan be used to replace damaged panels 10, if needed for an emergency,because they are interchangeable. The panels 10 can also be used withother types of panels, such as conventional wooden panels, and can beused to replace broken or damaged panels in other doors. The outsideface of the outside wall 14 of the panels can be molded with a simulatedwood grain to match or simulate wood door panels.

Referring now also to FIG. 5, the inside wall 12 of each panel 10includes outer open horizontal, longitudinally extending channels 20,inner open longitudinally extending horizontal channels 22, and verticalribs 24. The open longitudinally extending open channels 20, 22 extendtoward the outside wall 14 and form between them longitudinal,horizontal ribs 21 and 26. As seen in FIG. 5, thelongitudinally-extending channels 22 and 20 are fused to the outsidewall 14 of the panel. Vertical ribs 24 intersect the longitudinal,horizontal ribs 21 and 26 and the open, longitudinally extendingchannels 20 and 22. The outside wall 14 comprises a substantially Outouter surface of the panel 10. The end walls 16 are relatively flat andone of the end walls 16 includes an opening 30 (FIG. 2) adapted toreceive a nozzle (not shown), the purpose of which will be describedhereinafter. The top wall 18 comprises an open channel 32 spanning thelength thereof and extending a distance into the panel 10. The bottomwall 19 comprises a projection 34 spanning the length thereof andadapted for receipt within the channel 32. The channel 32 and projection34 can have any desired shape and configuration so long as theprojection 34 can be removably received by the channel 32 when thepanels 10 are vertically assembled into the door 44 or the like.Preferably, the projection 34 has a somewhat tapered shape to facilitatesmooth pivotal movement between two adjacent panels 10, such as theshape illustrated in FIG. 5. Although the panel 10 is described ascomprising inside wall 12 and outside wall 14, it is understood thatwhen in use, the orientation of the panel 10 can be reversed.

On the inside wall 12, the outer channels 20 and inner channels 22extend longitudinally across the panel 10 and have a length slightlyless than that of the panel 10. The outer channels 20 and inner channels22 also form ribs therebetween. Although the outer channels 20 areillustrated as having a relatively rectangular shape while the innerchannels 22 are illustrated as having a relatively ovular shape, theouter channels 20 and inner channels 22 can be formed having any desiredshape and can be formed in identical shapes. The outer channels 20 andinner channels 22 have a depth slightly less than that of the panel 10such that the inside wall 12 and outside wall 14 are fused along thedeepest portion of the channels 20, 22. Alternatively, the inside wall12 and outside wall 14 can be slightly spaced along the deepest portionof the channels 20, 22. The vertical ribs 24 extend across the innerchannels 22 and are oriented perpendicularly thereto. The vertical ribs24 can be spaced equidistantly as shown, or they can be spaced in anyother manner as desired. The vertical ribs 24 are approximately thedepth of the panel 10 such that when viewed from either end wall 16, thevertical ribs 24 cannot be seen.

With continued reference to FIG. 5, reinforcing cavities 38 are locatedwithin the interior of the panel 10 adjacent each of the channel 32 andprojection 34 at the top wall 18 and bottom wall 19, respectively. Thereinforcing cavities 38 are sized to receive reinforcing members 40therein in a secure manner, such as by a press fit or shrink fit, whichwill be discussed in more detail hereinafter.

The reinforcing members 40 comprise rigid bars having U-shaped crosssections that extend longitudinally along the length of the panel 10between the end walls 16. The reinforcing members 40 can be completelyenclosed by the panel 10. The reinforcing bars can be made of relativelystrong metal, such as steel, or of aluminum but can also be made of asuitable rigid or reinforced plastic material. An exemplary materialthat can be used to form the reinforcing members is a Martinisite,high-strength, high-carbon steel. The bars are stiffer than thethermoplastic material from which the panels 10 are molded. Thereinforcing members 40 can have any shape that, when inserted into thepanel 10, provides reinforcement to the panel 10. For example, thereinforcing members 40 can be solid aluminum rods having a circularcross section, or hollow iron bars having a square cross section. Thecavities 38 are sized such that they will shrink around the reinforcingmembers 40 during formation of the panel 10 as the panel 10 cools tofrictionally secure the reinforcing members 40 within the cavities 38.

Referring now to FIG. 6, each panel 10 is formed by blow molding ahollow panel in a mold. The mold is formed having a predominantlyrectangular exterior shape and comprises two mold halves. The interiorsof the mold halves are formed having the shape of the inside wall 12 andoutside wall 14 of the panel 10, respectively. A method 200 of blowmolding a panel 10 comprises a first step 202 in which a molten preformor parison is placed into the mold. Next, the mold halves are closed atstep 204. Air is then blown into the parison or preform by the nozzle atstep 206 through the opening 30 to expand the parison to fill the moldcavity to form an article in the shape of the mold with flashing, orexcess material, around the outside of the article. The channels 20, 22and vertical ribs 24 in the outside wall 12 of the panel 10 are formedin the panels 10 at step 206. Preferably, the channels 20, 22 extendinwardly toward the inside wall 14 of the panel 10 and are fused theretothrough heat and pressure. Before the panel 10 is cooled and while thepanel 10 is still warm, the panel 10 is removed from the mold at step208. At step 210, the flashing is removed from the outside of the panel10, and then at step 212, one end wall 16 is trimmed to provide openingsto the channels 38. Next, at step 214, while the panel 10 is still warm,the elongated U-shaped reinforcing members 40 are slid inside thechannels 38. The panel 10 is then cooled completely at final step 216.As the panel 10 cools, the panel 10 shrinks around the elongatedU-shaped reinforcing members 40 to lock the elongated U-shapedreinforcing members 40 into the panels 10.

Once the panels 10 have been formed, the door 44 can be assembled byinterconnecting the panels 10 using the hinges 50, 56 and rivets 52, 58,respectively, and bolts 55. The bracket 60 of the latch assembly 126 canalso be connected to the lowermost panel 10 at the bottom wall 19thereof by the bracket rivets 61, and the liners 62 can be connected tothe top wall 18 of the uppermost panel 10 and the bottom wall 19 of thelowermost panel 10. The axles of the roller assemblies 36 can beinserted into the sockets formed by the cap plate 54 and hinge body 53of each of the outer hinges 52. The rollers of the roller assemblies 36can then be positioned within the channel of the tracks to mount thedoor 44 to the trailer 100.

The invention remedies the problem of replicating a wooden roll-up doorpanel by providing a blow-molded a panel 10 with multiple cavitiesformed by a simple and efficient method 200. In addition, thereinforcing members 40 serve to prevent any warping of the panels 10 andhelp to strengthen the panels 10. The reinforced panels 10 can be usedto form durable and long-lasting roll-up doors 44. In addition, thepanels 10 according to the invention are sized to be interchangeablewith conventional wooden panels so that the panels 10 according to theinvention can replace a worn or damaged wooden panel and vice versa. Thepanels 10 can have a textured surface resembling a wooden surface. Thetextured surface can be formed during the molding process so that thepanels 10 look the same as wooden panels and thus can be used in a rollup door assembly that includes one or more wooden panels. As woodenpanels are currently used in a large number of roll-up doors and arewidely available, the interchangeability provided by the inventivepanels 10 conveniently allows damaged blow molded panels 10 to bereplaced by wooden panels if replacement blow molded panels 10 are notavailable.

The panels can be made from a variety of suitable moldable outdoorthermoplastic materials including polyolefin polymers (polyethylene,polypropylene) and copolymers and polyvinyl chloride polymers andcopolymers. The preferred material is a high density polyethylene withan extra high molecular weight, hexane copolymer sold, for example byChevron Phillips Chemical Company as MARLEX® HMX 50100, and having atensile strength at yield of 3,600 psi (25 MPa), Elongation at break of700%, Flexural modulus of 175,000 psi (1200 MPa), ECSR (condition A andB)>600 h, durometer hardness Type D 69, Vicat Softening Temperature 258°F. (126° C.), heat deflection temperature 173° F. (78° C.), BrittlenessTemperature <−103° F. (<−75° C.) and tensile impact 90 ft-lb/in² (190kJ/m²).

Although the present invention has been described in terms of specificexemplary embodiments, it will be appreciated that reasonable variationsand modifications are possible within the scope of the foregoingdisclosure and drawings without departing from the spirit of theinvention which is set forth in the following claims.

What is claimed is:
 1. A roll-up door comprising a plurality of panelsjoined together at upper and lower portions thereof with hinges andfurther comprising roller assemblies mounted to sides of the panels formounting the panels in channels for movement between an upper positionand a lower position, the improvement comprising at least some of thepanels are formed of thermoplastic material that is blow-molded intohollow panels that have a relatively flat outside wall and an insidewall, wherein the inside wall is characterized by longitudinal,horizontal ribs formed by open-sided, longitudinally extending channelsthat extend toward the outside wall and at least some of thelongitudinally-extending channels are fused to the outside wall of thepanels, and vertical ribs that intersect the horizontal ribs and extendthrough the open-sided, longitudinally extending channels; and thehinges are mounted to the thermoplastic blow-molded panels withfasteners that extend through the inside wall of the thermoplasticblow-molded panels.
 2. The roll-up door according to claim 1, whereinthe panels have elongated hollow channels that extend along the upperand lower portions of the panels and reinforcing members of a materialstiffer than the thermoplastic material are retained in the elongatedhollow channels, and the fasteners extend through the inside wall at theelongated hollow channels.
 3. The roll-up door according to claim 2,wherein the fasteners are rivets.
 4. The roll-up door according to claim2, wherein the reinforcing members are frictionally retained in theelongated channels by press fit into the elongated hollow channels, orby shrink fitting the elongated hollow channels onto the reinforcingmembers.
 5. The roll-up door according to claim 2, wherein the fastenerspenetrate the elongated channels, and the fasteners are rivets.
 6. Theroll-up door according to claim 5 wherein the reinforcing members areformed of a metal.
 7. The roll-up door according to claim 2 wherein thereinforcing members are formed of a plastic stiffer than thethermoplastic material.
 8. The roll-up door according to claim 1 whereinat least some of the hinges are positioned at the sides of the panelsand have sockets and the roller assemblies are mounted in the sockets.9. The roll-up door according to claim 1 wherein the panels haveelongated hollow channels that extend along the upper and lower portionsof the panels and reinforcing members of a material stiffer than thethermoplastic material are positioned in the elongated hollow channelsand are frictionally retained therein, and further wherein the fastenersextend through the inside wall of the elongated hollow channels.
 10. Theroll-up door according to claim 9 wherein the fasteners are rivets. 11.A panel for use in a roll-up door assembly comprising a plurality ofpanels directly joined together at top and bottom portions thereof withhinges and roller assemblies mounted to the panels for mounting thepanels in channels for movement between an upper position and a lowerposition, wherein the panel is formed of thermoplastic material that isblow-molded into a hollow form that has a relatively flat outside walland an inside wall, wherein the inside wall is characterized bylongitudinal ribs formed by open-sided, longitudinally extendingchannels that extend toward the outside wall and at least some of thelongitudinally-extending channels are fused to the outside wall of thepanel, and vertical ribs that intersect the longitudinal ribs and extendthrough the open-sided, longitudinally extending channels; elongatedhollow channels extending along the top and bottom portions of thepanel; and reinforcing members of a material stiffer than thethermoplastic material retained in the elongated hollow channels,wherein the top and bottom portions of the panel are configured toreceive fasteners for hinges to join the panel to adjacent panels toform the roll-up door assembly.
 12. The panel according to claim 11,wherein the elongated hollow channels are shrunk fit onto thereinforcing members to frictionally retain the reinforcing members inthe hollow channels.
 13. The panel according to claim 11, wherein thereinforcing members are press fit into the elongated hollow channels tofrictionally retain the reinforcing members in the hollow channels. 14.The panel according to claim 11 wherein the elongated hollow channelsare formed along both top and bottom walls of the panel.
 15. The panelaccording to claim 11 wherein the reinforcing members are formed of ametal.
 16. The panel according to claim 11 wherein the reinforcingmembers are formed of a plastic stiffer than the thermoplastic material.